Approaches for Stereotactic Radiosurgery (SRS)/Stereotactic Radiotherapy (SRT) in brain metastases using different radiotherapy modalities (Feasibility study).

BACKGROUND: SRS and SRT are precise treatments for brain metastases, delivering high doses while minimizing doses to nearby organs. Modern linear accelerators enable the precise delivery of SRS/SRT using different modalities like three-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT), and Rapid Arc (RA). OBJECTIVE: This study aims to compare dosimetric differences and evaluate the effectiveness of 3DCRT, IMRT, and Rapid Arc techniques in SRS/SRT for brain metastases. METHODS: 10 patients with brain metastases, 3 patients assigned for SRT, and 7 patients for SRS. For each patient, 3 treatment plans were generated using the Eclipse treatment planning system using different treatment modalities. RESULTS: No statistically significant differences were observed among the three techniques in the homogeneity index (HI), maximum D2%, and minimum D98% doses for the target, with a p > 0.05. The RA demonstrated a better conformity index of 1.14±0.25 than both IMRT 1.21±0.26 and 3DCRT 1.37±0.31. 3DCRT and IMRT had lower Gradient Index values compared to RA, suggesting that they achieved a better dose gradient than RA. The mean treatment time decreased by 26.2% and 10.3% for 3DCRT and RA, respectively, compared to IMRT. In organs at risk, 3DCRT had lower maximum doses than IMRT and RA, but some differences were not statistically significant. However, in the brain stem and brain tissues, RA exhibited lower maximum doses compared to IMRT and 3DCRT. Additionally, RA and IMRT had lower V15Gy, V12Gy, and V9Gy values compared to 3DCRT. CONCLUSION: While 3D-CRT delivered lower doses to organs at risk, RA and IMRT provided better conformity and target coverage. RA effectively controlled the maximum dose and irradiated volume of normal brain tissue. Overall, these findings indicate that 3DCRT, RA, and IMRT are suitable for treating brain metastases in SRS/SRT due to their improved dose conformity and target coverage while minimizing dose to healthy tissues.

Comparison of Progressive Resolution Optimizer and Photon Optimizer algorithms in RapidArc delivery for head and neck SIB treatments.

Background: The aim of this study is to analyze and verify characterization of two different algorithms using simultaneous integrated boost (SIB) in head and neck (H&N) plans. Materials and methods: In our study 15 patients were selected, who received radiation therapy by using Eclipse volumetric modulated arc therapy (VMAT) Progressive Resolution Optimizer (PRO) algorithm 15.1. The same cases were re-optimized using a Photon Optimizer (PO) algorithm 15.6.A total of 30 treatment plans (15 PRO-VMAT plans and 15 PO-VMAT plans) were produced in the present study. All plans were created using double full arcs, keeping the identical constraints, cost functions and optimization time. Plan evaluation was done using planning target volume (PTV) parameters (D98%, D95%, D50%, D2% mean dose and V105%), homogeneity index (HI), conformity index (CI), Monitor unit (MU) per degree with control points (CP), organ at risk (OAR) doses and gamma verification (Portal dosimetry and ArcCHECK) values were evaluated. Treatment was delivered in Varian Truebeam 2.5, energy 6 MV with Millennium 120 multileaf collimator (MLC). Results: The PTV coverage (D95%) for PRO and PO were 98.7 ± 0.8 Gy, 98.8 ± 0.9 Gy, HI were 0.09 ± 0.02 and 0.09 ± 0.02, CI were 0.98 ± 0.01 and 0.99 ± 0.01. Monitor units (MU) for PRO and PO were 647.5 ± 137.9, 655.2 ± 138.4. The Portal dose results were [3%, 3mm (%) & 1 %, 1 mm (%)] for PO and PRO 100 ± 0.1, 95.1 ± 1.4 and 100 ± 0.1, 95.2 ± 1.3. For ArcCHECK were 99.9 ± 0.1, 94.7 ± 3.0 and 99.9 ± 0.1, 93.5 ± 3.9, respectively. Conclusion: Results showed that PTV coverage and OAR doses were comparable. For individual patients CI and HI of PO showed slightly higher values than PRO. MUs for PO were slightly increased as compared to PRO. MU per degree with each individual control points generated by PO showed a high degree of modulation compared to PRO. Hence, new PO optimizer can produce a comparable degree of plan while using the same PRO objectives.

Dosimetric influence of filtered and flattening filter free photon beam on rapid arc (RA) radiotherapy planning in case of cervix carcinoma.

AIM: To investigate the dosimetric influence of filtered and flattening filter free (FFF) photon beam of 6 and 10 MV energies on cervix RA radiotherapy planning and to find possibilities to develop the clinically acceptable RA plans with FFFB photon beam and explore their potential benefits to cervix cancer patients. BACKGROUND: FFF photon beams enhances the treatment delivery by increased dose rate which results in shorter treatment time, this shorter treatment time reduces intrafraction motion and enhance comfort to the patients. MATERIALS AND METHODS: RA plans were generated for filtered and flattening filter free photon beams of 6 and 10 MV energies using same dose-volumes constraints. RA plans were generated to deliver a dose of 50.4 Gy in 28 fractions, for a cohort of eleven patients reported with cervix carcinoma. RA plans were evaluated in terms of PTV coverage, dose to OAR's, CI, HI, total no. of monitor units (MUs) and NTID and low dose volume of normal tissues. RESULTS: Clinically acceptable and similar plans were generated for filtered and flattening filter free photon beams. FFFB delivered slightly higher mean target dose (52.28 Gy vs. 52.0 Gy, p = 0.000 for 6 MV and 52.42 Gy vs. 52.0 Gy, p = 0.000 for 10 MV) less homogeneous (1.062 vs. 1.052, p = 0.000 for 6 MV and 1.066 vs. 1.051, p = 0.000 for 10 MV) and less conformal (1.007 vs. 1.004, p = 0.104 for 6 MV and 1.012 vs. 1.003, p = 0.010 for 10 MV) RA plans compared to FB. FFFB delivered more doses to the bladder and rectum, also required more numbers of MUs in comparison to FB. CONCLUSIONS: This study concludes that FB is more beneficial for cervix RA planning in comparison to FFFB, as FB generates more conformal and homogenous rapid arc plans and offers better OAR's sparing.

Is dose escalation achievable for esophageal carcinoma?

AIM: To investigate the feasibility of dose escalation using rapid arc (RA) and Helical Tomotherapy (HT) for patients with upper, middle and distal esophageal carcinomas, even for large tumor volumes. BACKGROUND: In esophageal cancer, for patients with exclusive radio-chemotherapy, local disease control remains poor. Planning study with dose escalation was done for two sophisticated modulated radiotherapy techniques: Rapid arc against Tomotherapy. MATERIALS AND METHODS: Six patients treated with a RA simultaneous integrated boost (SIB) of 60 Gy were re-planned for RA and HT techniques with a SIB dose escalated to 70 Gy. Dose volume histogram statistics, conformity indices and homogeneity indices were analyzed. For a given set of normal tissue constraints, the capability of each treatment modality to increase the GTV dose to 70 Gy was investigated. RESULTS: Either HT or VMAT may be used to escalate the dose delivered in esophageal tumors while maintaining the spinal cord, lung and heart doses within tolerance. Adequate target coverage was achieved by both techniques. Typically, HT achieved better lung sparing and PTV coverage than did RA. CONCLUSIONS: Dose escalation for esophageal cancer becomes clinically feasible with the use of RA and HT. This promising result could be explored in a carefully controlled clinical study which considered normal tissue complications and tumor control as endpoints.

Assessment of the Dosimetric Index from IMRT and Rapid arc Plan for Oropharyngeal Cancer with Simultaneous Integrated Boost (SIB) Technique in Combination with EUD-based NTCP and TCP Radiobiological Models.

PURPOSE: The current research compared radiobiological and dosimetric results for simultaneous integrated boost (SIB) plans employing RapidArc and IMRT planning procedures in oropharyngeal cancer from head-and-neck cancer (HNC) patients. MATERIALS AND METHODS: The indigenously developed Python-based software was used in this study for generation and analysis. Twelve patients with forty-eight total plans with SIB were planned using Rapid arc (2 and 3 arcs) and IMRT (7 and 9 fields) and compared with radiobiological models Lyman, Kutcher, Burman (LKB) and EUD (Equivalent Uniform Dose) along with physical index such as homogeneity index(HI), conformity index(CI) of target volumes. RESULTS: These models' inputs are the dose-volume histograms (DVHs) calculated by the treatment planning system (TPS). The values obtained vary from one model to the other for the same technique and patient. The maximum dose to the brainstem and spinal cord and the mean dose to the parotids were analysed both dosimetrically and radiobiologically, such as the LKB model effective volume, equivalent uniform dose, EUD-based normal tissue complication probability, and normal tissue integral dose. The mean and max dose to target volume with conformity, homogeneity index, tumor control probability compared with treatment times, and monitor units. CONCLUSION: Rapid arc (3 arcs) resulted in significantly better OAR sparing, dose homogeneity, and conformity. The findings indicate that the rapid arc plan has improved dose distribution in the target volume compared with IMRT, but the tumor control probability obtained for the two planning methods, Rapid arc (3 arcs) and IMRT (7 fields), are similar. The treatment time and monitor units for the Rapid arc (3 arcs) were superior to other planning methods and considered to be standard in head & neck radiotherapy.

A dosimetric comparison of intensity-modulated radiotherapy versus rapid arc in gynecological malignancies: Dose beyond planning target volume, precisely 5Gy volume.

Introduction: Aim of radiotherapy is precise dose delivery with objective of achieving maximum local control and minimal toxicity by decreasing dose to organ at risk (OAR).This aim can be achieved by technologies like intensity-modulated radiotherapy (IMRT) and volumetric arc therapy. However, later offers comparable or even better plan quality with shorter treatment time. It is important to note that low dose regions are also a concern due long-term risk of developing a second cancer after radiotherapy. The objective of our study is to do dosimetric comparison of IMRT vs. Rapid arc (RA) plan in gynecology cancer and specifically to assess dose beyond planning target volume (PTV), precisely 5 Gy volume. Methods: Each 20 eligible patients underwent radiotherapy planning on eclipse by both IMRT and RA plans as per institution protocols. Comparative dosimetric analysis of both plans was done by paired sample t-test. PTV metrics compared were D95%, homogenecity index (HI), and conformity index (CI). OAR dose compared were bowel V40 Gy <30%, Rectum V30 Gy <60%, Bladder V45 Gy <35%, and bilateral femur head and neck V30 Gy < 50%. Futhermore, calculated monitor units (MUs) were also compared. Finally, volume of normal tissue beyond the PTV, specifically 5 Gy volume, was compared between plans. Results: Dosimetric plan comparison showed statistically significant difference in RA and IMRT plans with improved PTV coverage and better OAR tolerance with RA plan. In addition, MU used were significantly less in RA plan, coupled with reduced V5 Gy volume. Conclusion: In sum, RA plans are dosimetrically significantly better compared to IMRT plans in gynecological malignancies in terms of PTV coverage and OAR sparing. Importantly, not only less MU used but also significantly less normal tissue V5 Gy volume is less in RA compared to IMRT plans.

Role of rapid arc-image-guided radiotherapy in hepatocellular carcinoma with portal vein tumor thrombosis: A study from tertiary care center in Punjab, India.

Background and Objectives: Treatment of hepatocellular carcinoma (HCC) with portal vein tumor thrombus (PVTT) is very challenging with poor outcome. In this situation, radiotherapy has become an alternative treatment modality, more precisely due to advances in radiation techniques. The goal of our study is to do analysis of these patients treated with rapid arc image-guided technology (RA-IGRT) at our institution. Materials and Methods: Thirteen patients were included in the study. As per intuition policy, patient set up, contouring, and treatment plans were generated. Radiological response assessment was done 1-month post-radiotherapy. Survival analysis curve along with Chi-square test for prognostic factors assessment was done using SPSS. Results: With median dose of 45 Gy in 20 fractions, we were able to achieve 27.3% objective response rate with median survival of 5 months in eligible patients. Conclusions: One-year overall survival up to 30% can be achieved in HCC with PVTT, especially in patients with objective response to radiotherapy with Japan Integrated Staging score 2, provided it is precisely hit by RA-IGRT.

Analysis of Rapid arc-based Radiation Therapy on Dosimetric Parameters in Cervical Cancer Patients with and without Bone Marrow Sparing.

BACKGROUND: The standard treatment for cervical cancer is chemoradiation therapy. Pelvic radiation is associated with higher dose to bone marrow (BM) causing interrupted treatment due to haematologic toxicity with inferior outcomes. This study aims to evaluate rapid arc technique in sparing pelvic BM and dosimetric parameters for pelvis V5GY, V10GY, V20GY, V30GY, and V40GY dose. METHOD: Twenty one cervical cancer patients were selected for the analysis. Planning target volume (PTV) contours, total pelvic BM and surrounding structures contours were standardised. Two rapid arc based procedures were designed for individual patient. One was done using bone marrow sparing (BMS) constraints while other was performed without BMS constraints. Data for both plans was calculated with regard to PTV, normal structures and pelvic BM. Difference in dose distribution in both groups was analysed using Wilcoxon and Friedman ANOVA test. RESULTS: In the presence of BM constraint a significant changes in pelvic BM dose for values of V10GY (p=0.002), V20GY (p=0.002) and V40GY (p=0.025) was observed. The coverage of PTV was found to be unaffected by adding BM constraint. CONCLUSION: The BM is radiosensitive structure so dosage is linked with haemtological toxicity. Increased dose is associated with higher grade of haematological toxicity in pelvic radiotherapy. The study suggests that adding BM constraint in plans reduced the pelvic BM dose while not affecting PTV coverage and dose to bowel, bladder and rectum. Bone marrow constraint in pelvic radiotherapy can be considered for better treatment toleration and to determine its role in decreasing haematological toxicity.

The patient-reported outcome measures in oropharyngeal, laryngeal and hypopharyngeal cancer patients treated with Volumetric Modulated Arc based simultaneous integrated boost radiotherapy.

OBJECTIVE: To assess the change in the quality of life (QOL) in head and neck cancer patients treated with Simultaneous Integrated Boost (SIB) by Volumetric Modulated Arc Therapy (VMAT) technique. METHODS: Thirty patients with localised head and neck cancers (Stage II- IVa) were treated with VMAT and SIB technique. The three-dose levels prescribed were 68.2 Gy at 2.2 Gy/fraction, 62 Gy at 2 Gy/fraction and 55.8 Gy at 1.8 Gy/fraction to the high, intermediate and low-risk volumes respectively. Concurrent chemotherapy with cisplatin 100 mg/m2 was administered once in three weeks. Acute toxicities were evaluated and scored according to the RTOG grading system. Quality of life (QOL) was assessed using European Organization of Research and Treatment of Cancer (EORTC) QLQC30 and HN35 questionnaires at baseline and in three instances (immediately, one month and three months after the radiotherapy). RESULTS: Out of the total 30, 80% patients had a complete response (CR) at the median follow up of 12 months, while three patients died because of progression, and the remaining 3 had stable disease. All planning objectives were achieved for organs at risk and planning target volume(PTV). There was a statiscally significant(p value < 0.001) reduction in global quality of life scores at the end of treatment when compared to baseline scores, but by three months, there was the return in the QOL scores in most scales similar to the baseline value. CONCLUSION: VMAT based Simultaneous boost radiotherapy is a feasible and safe strategy in terms of toxicity profile with an acceptable transient change in the quality of life and allows a faster return to baseline quality of life.

A radiobiological and dosimetrical comparison between simultaneous integrated and sequential boost intensity-modulated arc treatment of locally advanced head-and-neck cancer.

PURPOSE: The study aimed to compare the radiobiological and dosimetric parameters between sequential boost (SEQB) and simultaneous integrated boost (SIB) treatment regimen using intensity-modulated arc therapy technique in locally advanced head-and-neck cancer (LAHNC) patients. MATERIALS AND METHODS: A total of 24 previously untreated LAHNC patients were randomized into SIB (n= 11) and SEQB (n = 13) arms. The planning computed tomography data set was transferred to the treatment planning system. All the target volumes and organ at risk volumes were delineated. Single plan for SIB group and three plans (three phases) were generated for SEQB group of patients. Radiobiological and dosimetric parameters were compared. RESULTS: The BED10(planned) value for high-risk (HR) planning target volume (PTV) was same in both groups, whereas for intermediate-risk (IR) PTV and low-risk (LR) PTV, the values were higher in SEQB arm than SIB arm. The V95 values were 100% for all the target volumes in both arms of patients. The average D100 value for gross target volume, HR PTV, and IR PTV was higher in SEQB arm than that in the SIB arm. The average D100 value for LR PTV was higher in the SIB arm compared to that of the SEQB arm. The BED10(achieved) was calculated using D100 values of target volumes. The difference of BED10(achieved) values between SEQB arm and SIB arm further increased than the BED10(planned) values for all target volumes. The maximum doses for spinal cord, spinal cord planning risk volume, and brain stem were within the tolerance dose in both groups of patients. The left and right parotid glands sparing was comparable in both groups of patients. Average integral dose was higher in the SIB group than SEQB group. The average total monitor unit per fraction was higher in the SEQB arm than that in the SIB arm. CONCLUSION: SIB regimen may be considered as more logical and efficient over SEQB regimen in the treatment of LAHNC with comparable radiobiological and dosimetric parameters.

Proton therapy- the modality of choice for future radiation therapy management of Prostate Cancer?

BACKGROUND: Proton Therapy (PR) is an emerging treatment for prostate cancer (Pca) patients. However, limited and conflicting data exists regarding its ability to result in fewer bladder and rectal toxicities compared to Photon Therapy (PT), as well as its cost efficiency and plan robustness. MATERIALS AND METHODS: An electronic literature search was performed to acquire eligible studies published between 2007 and 2018. Studies comparing bladder and rectal dosimetry or Gastrointestinal (GI) and Genitourinary (GU) toxicities between PR and PT, the plan robustness of PR relative to motion and its cost efficiency for Pca patients were assessed. RESULTS: 28 studies were eligible for inclusion in this review. PR resulted in improved bladder and rectal dosimetry but did not manifest as improved GI/GU toxicities clinically compared to PT. PR plans were considered robust when specific corrections, techniques, positioning or immobilisation devices were applied. PR is not cost effective for intermediate risk Pca patients; however PR may be cost effective for younger or high risk Pca patients. CONCLUSION: PR offers improved bladder and rectal dosimetry compared to PT but this does not specifically translate to improved GI/GU toxicities clinically. The robustness of PR plans is acceptable under specific conditions. PR is not cost effective for all Pca patients.

Multi-isocenter hybrid electron and rapid arc photon treatment for reirradiation of extensive recurrent inflammatory breast cancer.

Delivering an adequate and homogenous dose to a large volume of recurrent cutaneous disease can be challenging even with modern techniques. Here, the authors describe a 3-isocenter hybrid electron and rapid arc photon radiation treatment plan to provide optimal tumor coverage to an extensive recurrence of inflammatory breast carcinoma. This approach allowed for homogeneous treatment of a large volume while effectively modulating dose to previously irradiated tissue and minimizing dose to the underlying heart, lungs and brachial plexus.

Pencil beam scanning proton therapy vs rotational arc radiation therapy: A treatment planning comparison for postoperative oropharyngeal cancer.

Patients diagnosed with head and neck cancer are traditionally treated with photon radiotherapy. Proton therapy is currently being used clinically and may potentially reduce treatment-related toxicities by minimizing the dose to normal organs in the treatment of postoperative oropharyngeal cancer. The finite range of protons has the potential to significantly reduce normal tissue toxicity compared to photon radiotherapy. Seven patients were planned with both proton and photon modalities. The planning goal for both modalities was achieving the prescribed dose to 95% of the planning target volume (PTV). Dose-volume histograms were compared in which all cases met the target coverage goals. Mean doses were significantly lower in the proton plans for the oral cavity (1771cGy photon vs 293cGy proton, p < 0.001), contralateral parotid (1796cGy photon vs 1358 proton, p < 0.001), and the contralateral submandibular gland (3608cGy photon vs 3251cGy proton, p = 0.03). Average total integral dose was 9.1% lower in proton plans. The significant dosimetric sparing seen with proton therapy may lead to reduced side effects such as pain, weight loss, taste changes, and dry mouth. Prospective comparisons of protons vs photons for disease control, toxicity, and patient-reported outcomes are therefore warranted and currently being pursued.

Treatment Planning With Unflattened as Compared to Flattened Beams for Bilateral Carcinoma of the Breast

Aim: To evaluate the plan quality of 6MV unflattened (UFB) and flattened beam (FB) photon energy using AAA dose calculation algorithms for volumetric arc therapy. Materials and Methods: Plans were generated for bilateral carcinoma of breast and the dose prescribed was 50.4Gy in 28 fractions. Two different plans were made for each patient using 6MV FB and 6MV UFB. Dose calculations were performed on an AAA dose calculation algorithm. Plans were generated on Eclipse TPS and were capable of being delivered with a true beam STx linear accelerator. The homogeneity index (HI), conformity index (CI), normal tissue integral dose (NTID), and effect of low dose volume on normal tissue and monitor units (MU) were noted. Results: All the plans were clinically acceptable. The HI and CI of 6MV UF rapid arc (RA) plans were higher than with the 6MV FB plan (1.16±0.05 and 0.12±0.00 respectively). There was no appreciable difference observed in Organ at risk (OAR) doses. The mean NTID and low dose volume were significantly low with 6MV RA UFB as compared to FB. 6MV RA UFB required a 35% higher MU than with the 6MV RA plan (p<0.05). Conclusion: RA plans generated with UFB on Eclipse TPS achieved target volume coverage and preserved OAR's essentially similar to 6MV RA FB plans. However RA plans generated in Varian Eclipse of UFB were superior with respect to mean NTID and low dose volumes in normal tissue.

Comparison of Rapid Arc and Intensity-modulated Radiotherapy Plans Using Unified Dosimetry Index and the Impact of Conformity Index on Unified Dosimetry Index Evaluation.

The aim of this study was to evaluate the impact of conformity index in the unified dosimetry index (UDI) score for two different planning techniques namely intensity-modulated radiotherapy (IMRT) and Rapid Arc. Rapid Arc and IMRT plans of 57 patients were evaluated and compared using UDI score which incorporates four indices. To determine the impact of conformity index on the IMRT and Rapid Arc plans, UDI at conformity index one of all plan (UDIunit_CI) score was calculated by assuming conformity index is equal to one. Mean and standard deviations of all indices were calculated. Rapid Arc technique plans of different treatment sites of all patients scored lesser UDI than IMRT plans, and the conformity index of Rapid Arc plan was significantly better than IMRT plan. The average dose gradient, homogeneity, coverage, and conformity index of all sites with Rapid Arc plans were 0.212 ± 0.05, 1.123 ± 0.03, 0.959 ± 0.03, and 1.056 ± 0.09; with IMRT plans were 0.190 ± 0.05, 1.113 ± 0.04, 0.950 ± 0.04, and 1.172 ± 0.16, respectively. UDI score value with actual conformity index of Rapid Arc and IMRT plans differed significantly (P < 0.001). However, UDIunit_CI score values with assumed conformity index equal to one did not differ significantly (P = 0.528). In the comparison of IMRT and Rapid Arc plans using the UDI score, the impact of conformity index was significant.

Dosimetric comparison of flattened and unflattened beams for stereotactic body radiation therapy: Impact of the size of the PTV on dynamic conformal arc and volumetric modulated arc therapy.

PURPOSE: Flattening filter free (FFF) beams are frequently used for stereotactic body radiation therapy with various treatment modalities: conventional static fields, dynamic conformal arc (DCA) or Rapid Arc (RA). The goal of this study was to obtain some criteria to enable a conscious choice of the employment of FFF beams and of the DCA or RA technique, depending on the PTV size. METHODS AND MATERIALS: 24 PTVs from 1.52cm3 to 445.24cm3 were studied in various sites: virtual phantom, lung and liver. For each PTV, DCA and RA plans were prepared using two flattened (FF) and two unflattened photon beams. Parameters such as conformity index, gradient index, healthy-tissue and organs at risk mean doses, number of monitor units (MU), beam on time (BOT) were used to quantify obtained dose distributions. Friedman tests and Spearman's rank correlation coefficients were also performed. RESULTS: No significant differences were found between FF and FFF beams for RA regarding conformity and gradient indices. For DCA, 10FFF is less suitable and forward planning becomes more challenging as PTV volume increases. FFF beams provided a better sparing of healthy-tissues except for 10FFF used with DCA. 6FFF was slightly better than 10FFF in terms of healthy-tissue mean doses. FFF beams generated significantly reduced BOTs and increased MUs. These effects were more pronounced for larger volumes and especially for RA plans. CONCLUSIONS: FFF showed better results than FF beams for the considered plans. 10FFF used with DCA should be used with caution for medium and large volumes.

Is high-dose rate RapidArc-based radiosurgery dosimetrically advantageous for the treatment of intracranial tumors?

In linac-based stereotactic radiosurgery (SRS) and radiotherapy (SRT), circular cone(s) or conformal arc(s) are conventionally used to treat intracranial lesions. However, when the target is in close proximity to critical structures, it is frequently quite challenging to generate a quality plan using these techniques. In this study, we investigated the dosimetric characteristics of using high-dose rate RapidArc (RA) technique for radiosurgical treatment of intracranial lesions. A total of 10 intracranial SRS/SRT cases previously planned using dynamic conformal arc (DCA) or cone-based techniques have been included in this study. For each case, 3 treatment plans were generated: (1) a DCA plan with multiple noncoplanar arcs, (2) a high-dose rate RA plan with arcs oriented the same as DCA (multiple-arc RA), and 3) a high-dose rate RA plan with a single coplanar arc (single-arc RA). All treatment plans were generated under the same prescription and similar critical structure dose limits. Plan quality for different plans was evaluated by comparing various dosimetric parameters such as target coverage, conformity index (CI), homogeneity index (HI), critical structures, and normal brain tissue doses as well as beam delivery time. With similar critical structure sparing, high-dose rate RA plans can achieve much better target coverage, dose conformity, and dose homogeneity than the DCA plans can. Plan quality indices CI and HI, for the DCA, multiple-arc RA, and single-arc RA techniques, were measured as 1.67 ± 0.39, 1.32 ± 0.28, and 1.38 ± 0.30 and 1.24 ± 0.11, 1.10 ± 0.04, and 1.12 ± 0.07, respectively. Normal brain tissue dose (V12Gy) was found to be similar for DCA and multiple-arc RA plans but much larger for the single-arc RA plans. Beam delivery was similar for DCA and multiple-arc RA plans but shorter with single-arc RA plans. Multiple-arc RA SRS/SRT can provide better treatment plans than conventional DCA plans, especially for complex cases.

Quality assurance of rapid arc treatments: performances and pre-clinical verifications of a planar detector (MapCHECK2).

The purpose of this study is to evaluate the use of MapCHECK2 in a patient-specific quality assurance (QA) procedure for Rapid Arc (RA) radiotherapy and to obtain reference values of gamma index (γ) for different irradiation geometries. Dose distributions of 386 patients, optimized with Eclipse treatment planning system for RA on Varian Clinac 2300IX were exported and measured with MapCHECK2 detector array inserted in a MapPHAN dedicated phantom. Gamma index analysis was used to evaluate differences between calculated and delivered doses; collected data were analysed on the basis of complexity of plans and type of disease. Angular dependence and dose drift of detectors were estimated. The overall mean passing rate (percentage of points with γ < 1) was equal to 97.0% ± 3.1%; plan-specific evaluation of %γ < 1 showed significant differences among different treatment protocols (pancreas 98.6% ± 1.5%, prostate 96.6% ± 2.8% and rectum 92.8% ± 5.7%). MapCHECK2 demonstrated a strong angular dependence over a restricted range of angles (90° ± 5° and 270° ± 5°); this condition affected the result of pre-treatment QA only for plans with intense lateral fluence. The drift of diode array response due to the accumulated dose was found to be comparable with the manufacturer's declaration (0.5% per 1000 Gy). MapCHECK2 proved to be a useful and accurate tool in the process of patient-specific QA for RA treatment. Excluding the irradiation geometries with a high contribution of lateral fluence, the mean percentage of cases with γ-index > 95% equal to 90.3% was obtained instead of 81.7% including all plans.

[Impact of dynamic IMRT and tomotherapy in pelvic cancers: a prospective dosimetric study with 51 patients]. / Apport de la RCMI rotationnelle et de la tomothérapie hélicoïdale dans les cancers pelviens : étude dosimétrique prospective sur 51 patients.

PURPOSE: To compare the dosimetric results of different techniques of dynamic intensity modulated radiation therapy (IMRT) in patients treated for a pelvic cancer with nodal irradiation. PATIENTS AND METHODS: Data of 51 patients included prospectively in the Artpelvis study were analyzed. Thirty-six patients were treated for a high-risk prostate cancer (13 with helical tomotherapy, and 23 with Rapid'Arc(®)) and 15 patients were treated for a localized anal cancer (nine with helical tomotherapy and six with Rapid'Arc(®)). Plan quality was assessed according to several different dosimetric indexes of coverage of planning target volume and sparing of organs at risk. RESULTS: Although some dosimetric differences were statistically significant, helical tomotherapy and Rapid'Arc provided very similar and highly conformal plans. Regarding organs at risk, Rapid'Arc(®) provided better pelvic bone sparing with a lower non-tumoral integral dose. CONCLUSION: In pelvis cancer with nodal irradiation, Rapid'Arc and helical tomotherapy provided very similar plans. The clinical evaluation of Artpelvis study will verify this equivalence hypothesis.

Investigation on the effect of sharp phantom edges on point dose measurement during patient-specific dosimetry with Rapid Arc.

The objective of this work was to investigate and quantify the effect of sharp edges of the phantom on the point dose measurement during patient-specific dosimetry with Rapid Arc (RA). Ten patients with carcinoma of prostate were randomly selected for this dosimetric study. Rapid Arc plans were generated with 6 MV X-rays in the Eclipse (v 8.6.14) with single arc (clockwise). Dosimetry verification plans were generated for two phantoms (cylindrical and rectangular). The cylindrical phantom was solid water (diameter 34 cm) and the rectangular phantom was a water phantom (25 cm × 25 cm × 10 cm). These phantoms were pre-scanned in computed tomography (CT) machine with cylindrical ionization chamber (FC65) in place. The plans were delivered with Novalis Tx linear accelerator with 6 MV X-rays for both the phantoms separately. The measured dose was compared with the planned dose for both the phantoms. Mean percentage deviation between measured and planned doses was found to be 4.19 (SD 0.82) and 3.63 (SD 0.89) for cylindrical and rectangular phantoms, respectively. No significant dosimetric variation was found due to the geometry (sharp edges) of the phantom. The sharp edges of the phantom do not perturb the patient specific Rapid Arc dosimetry significantly.